No Swiss fighter jets were scrambled Monday when an Ethiopian Airlines co-pilot hijacked his own plane and forced it to land in Geneva, because it happened outside business hours, the Swiss airforce said.

When the co-pilot on flight ET-702 from Addis Ababa to Rome locked himself in the cockpit while the pilot went to the bathroom and announced a hijacking, Italian and French fighter jets were scrambled to escort the plane through their respective airspaces.

But although the co-pilot-turned-hijacker quickly announced he wanted to land the plane in Switzerland, where he later said he aimed to seek asylum, Switzerland's fleet of F-18s and F-5 Tigers remained on the ground, Swiss airforce spokesman Laurent Savary told AFP.

This, he explained, was because the Swiss airforce is only available during office hours. These are reported to be from 8am until noon, then 1:30 to 5pm.

"Switzerland cannot intervene because its airbases are closed at night and on the weekend," he said, adding: "It's a question of budget and staffing."

Monday's hijacking, carried out by 31-year-old Hailemedehin Abera Tagegn, according to Addis Ababa, took place in the very early hours, with the aircraft and its 202 passengers and crew landing safely in Geneva at 6:02 am (0502 GMT).

That was just two minutes after the airport opened for business, and two hours before the Swiss airforce is operational.

Savary said Switzerland relies heavily on deals with its neighbours, especially France, to help police its airspace outside regular office hours.

He explained that French fighters can escort a suspicious aircraft into Swiss airspace, "but there is no question of shooting it down. It's a question of national sovereignty".

Swiss airspace is under constant electronic surveillance, he pointed out, adding that the wealthy Alpine nation is also studying the possibility of expanding its airforce coverage to a round-the-clock operation.

That plan is however not set to kick into action until 2020, when Switzerland is expected to replace its fleet of fighters with Swedish Gripen planes.

The purchase of the Swedish planes meanwhile rely on whether it is approved in an upcoming popular vote, with a poll published Monday showing 53 percent of Swiss oppose the deal.